Field
This disclosure relates generally to radio frequency receivers, and more specifically, to dynamic impairment compensation in direct conversion (DC) radio frequency receivers.
Related Art
Direct conversion receivers (DCRs) convert a radio frequency (RF) carrier waveform directly to baseband. Optimal signal reception requires the receiver gains, linearity, I and Q signal gain and phase mismatch, direct current voltage (DC) offsets and tuning parameters to be setup accurately for accurate reception of the down-converted antenna signal. Receiver impairments such as inadequate carrier suppression, second order inter-modulation, device level mismatches and inherent offsets in the active circuits of the receiver front end all contribute to a DC offset bias level in the down-converted baseband signal that needs to be corrected or compensated. Similarly, in-phase/quadrature (I/Q) path mismatches such as local oscillator (LO) generated noise (or equivalent), mismatches between I/Q path circuits and parasitics, and gain mismatches between I/Q path baseband circuits and data converters exhibit as IQ phase and gain imbalance.
Such DCR artifacts can seriously impede normal operation of a receiver by causing saturation and creating race conditions for transceiver state machines resulting in, e.g., automatic gain control failure, calibration out-of-range, ADC dynamic range wastage and/or incorrect demodulation and hence incorrect symbol recovery by a modem.
Receiver artifacts on silicon are implementation dependent and are impacted by the process technology node, layout, routing parasitics as well as specific circuit topology. In addition, the receiver impairments tend to be a function of process, voltage, temperature, RF frequency as well as external board level factors such as PCB layout and components.
DCR operation requires a highly coordinated factory trim, calibration, compensation and sequencing strategy for successful reception over a range of operational parameters.
Embodiments of the present invention are illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements, unless otherwise noted. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.